Be it known that I, \VILLIAM A. LORENZ, a citizen of the l nited States, residing at Hartford, in the county of Hartford and State of Connecticut, have invented a new and useful Improvement in Suction-Heads for Disk Grinding-Machines, of which the following is a specification.

This invention relates to the construction of the rotatory head of a grinding or polishing machine in which the abrasive in the form of a sheet or disk is held to the head by exhausting air from the head back of the abrasive.

The object of the invention is to provide a head for a machine of this character which can be used to retain abrasive sheets or disks of diii'erentsizes and which is screened to prevent dust or grains of abrasive from being drawn back into the air exhausting apparatus.

This object is attained by providing the abrasive holding face of the head with inner and outer series of openings or recesses, which series are independent of each other but which communicate with a central recess that communicates with the exhaust opening and that can be easily screened. The central recess is provided with a valve which may be set so that both the inner and outer series of openings will communicate sive material.

plane indicated by the dotted line 6-6 on with the exhaust opening, as when a large abrasive sheet is being used, or can be set so that only the inner series of openings will be in communication with the exhaust opening, as when a small abrasive sheet is being used.

In the accompanying drawings Figure 1 shows a face view of a suction head that embodies the invention, with a portion of a large abrasive sheet held thereon torn awayithe valve being adjusted so the head will hold an abrasive sheet of large size. Fig. 2 shows a section of the same on the dotted line 2-2 on Fig. 1. Fig. 3 shows a face view of the suction head with the valve adjusted for holding a small abrasive-sheet. Fig. 4 shows a section on the dotted line 1-4 on Fig. 3. Fig. 5 shows on larger scale a section of a, portion of the head, illustrating the relation of the parts when adjusted for holding a large sheet of abra- Fig. 6 is a section on the Fig. 5. Fig. 7 is a section showing the relation of the parts when the head is adjusted for holding a small abrasive sheet. Fig. 8 is a section on the plane indicated by the dotted line 8-S on Fig. 7.

The head illustrated. is a circular disk 10 with a hub 11 that is secured to the end of a hollow, rotatory shaft 12 to which any common form of air exhausting means may be connected in the ordinary way.

The head has a central recess 13 that com municates with the opening in the shaft, and extending outwardly from this central recess to near the closed outer rim li, where they open through the working face of the head, are channels 15. Also extending outwardly from the central recess are channels 16. These latter channels, however, are on a different plane from the channels 15 and they terminate near the annular surface 17 that is some distance in from the outer rim. This construction provides a working face in one plane for backing the abrasive sheet which comprises the face of the closed outer rim 14, the lands 18 between the outer ends of the channels 15,. the annular surface 17, and the lands 19 between the channels 16.

A circular valve 20 is'located in the central recess 13 and held in position by screws 21 that extend through slots 22 in the bottom of the valve into the body of the head. If these screws are loosened the valve may be turned and when the screws are tightened the valve is secured in the position to which it is turned. The outer edge of the valve is provided with ports 23. When the valve is turned to one position the ports )rovide communication between the inner ends of all of the channels 15 and all of the channels 16 and the central recess in the head (Figs. 5 and 6), and when the valve is turned to its other position the ports only connect the inner ends of the channels 16 with the central recess, the inner ends of the channels 15 under this condition being closed from the central recess (Figs. 'i' and 8).

A screen 24 is placed between the back of the valve and the head in the bottom of the central recess and over the exhaust openhausted from the head the abrasive sheet is retained at the center by the clamp and is held close to the entire working face of the head by the excess air pressure on the front, as shown in Fig. 1. If a small abrasive sheet is to be used the valve is turned to the position illustrated in Figs. 7 and 8. In this case the outer channels are closed and the inner channels are open to the. central recess. Then when air is exhausted from the head the small sheet is retained\by the central clamp and is held close against the lands between the inner channels and the annular surface which surrounds them, as shown in Fig. 3.

The invention claimed is 1. A suction head for a disk grinding or polishing machine, having a central opening and channels leading outwardly therefrom to different-distances from the central opening, and a valve adjustably mounted on the head and controlling communication between said central opening and said chan-. nels, whereby communication may be established between the central opening and all of the channels or only a part of the channels.

2. A suction head for a disk grinding or polishing machine having a central recess and channels that extend outwardly from the central recess and open through the working face of the head at different distances from the center, and avalve located in the central recess and adapted to open communication between all of the channels and the central recess or close communication between the. central recess and the channels that open farthest outward.

3. The suction head described by claim 2 characterized by having the head mounted on a hollow shaft the opening in which communicates with the central recess.

4. The suction head described by claim 2 eas es characterized by having a damp located in a depression in said valve.

5; The suction head described by claim 2 characterized by ha ving a screen located in the central recess between the valve and the head.

6. A suction head for a disk grinding or polishing machine having a working face in one plane and comprised of an annular surface near the outer rim, an annular surface intermediate the outer rim and the center, lands between the said annular surfaces and lands between the inner annular surface and the center of the head, said head also having a recess at the center-that communicates with the openings between said lands, and means located in said recess for closing communicationbetween'the recess and'the openings between the first mentioned lands.

7. A suction head for a disk grinding or polishing machine having openings in its front face and an opening through its back in communication with the openings in the front face whereby air may be exhausted from the openings in the front face through the opening in the back when an abrasive disk is placed over said front openings, and a screen covering said opening through the back for preventing dust and grains of sand from being sucked through the opening in the back of the head. i

8. A suction head for a disk grinding or polishing machine,'\ having passages that lead outwardly from thecenter and open through the working face of the head at different distances from the center, and a valve located on the face of the head and adapted to open communication through all of the passages orclose communication through the passages that open farthest outward. r